<?php	
//1.检索出每篇文章对应的标签
select a.atitle,t.tname from arc a join arc_tag at on a.aid=at.aid join tag t on at.tid=t.tid;
//2.将stu表中id=6的数据：性别改为女，年龄改为30
update stu set age=30,sex='女' where sid=6;
//4.删除年纪最小的同学
//6.给stu表添加一个time字段     int(8)
alter table stu drop time;
alter table stu add time int(8);
//7.将name 字段修改为varchar(30)
//8.删除学生表的主键
alter table stu modify sid int unsigned;
alter table stu drop primary key;
//9.给student表添加主键自增
//10.查找姓李同学的总数
//11.student表和class表，统计每个班有多少学生
select * from stu s join class c on s.cid=c.cid; 
select count(*),cname from stu s join class c on s.cid=c.cid group by cname;
//12.查找张国宝的同班同学(不包含张国宝)
//13.检索出【宝宝心里苦】这篇文章 有哪些标签
//14.查找所有90后的同学







